KR100977942B1 - Compensation device and method, flexible display and portable device - Google Patents

Abstract

The present invention provides a gray level compensation mechanism for flexible displays. Flexible displays show cell gap changes upon bending. This cell gap is measured during operation of the display (capacitive, piezoelectric). The pixel voltage is adjusted in accordance with the measured cell gap. As a result, gray levels occur regardless of the local bending radius.

Description

Compensation device and method, flexible display and portable device {LUMINESCENCE AND COLOR VARIATION COMPENSATION IN A FLEXIBLE DISPLAY}

The present invention relates to a device for compensating for light emission and / or color change in a voltage driven flexible display, the change being related to the bending of the flexible display, the device comprising at least a portion of the flexible display. Measuring means for measuring the cell gap in some, and adjusting means for adjusting the voltage applied to said portion of the flexible display depending on the measured cell gap.

The invention also relates to a flexible display comprising such a device and a portable device comprising such a flexible display.

The present invention also relates to a method for compensating for light emission and / or color change in a voltage driven flexible display, wherein the change is related to the bending of the flexible display, and the method relates to a flexible display. Measuring at least in part a cell gap and adjusting a voltage applied to said portion of the flexible display according to the measured cell gap.

Liquid crystal displays (LCDs) are devices that display text or images by transmitting or blocking light by controlling an electric field applied to a liquid crystal material having dielectric anisotropy, all of which are well known to those skilled in the art and are briefly described. Explain. Unlike display devices that generate light internally, such as electroluminescent (EL) devices, cathode ray tubes (CRTs), and light emitting diodes (LEDs), LCDs use external light sources.

LCD devices are largely classified into transmissive devices and reflective devices according to the method of using light. In addition to the liquid crystal panel having a liquid crystal mixture injected between two transparent substrates, the transmissive LCD further includes a backlight device for supplying light to the liquid crystal panel. However, it is very difficult to produce a transmissive LCD having a thin thickness and a light weight.

Reflective LCDs, on the other hand, include reflective liquid crystal display panels that transmit and reflect natural and ambient light to the display screen without a backlight device.

Basic liquid crystal displays can be easily constructed by coating two thin sheets of transparent material such as glass or plastic with transparent metal oxide. Preferably, metal oxides are applied in parallel form on each separate sheet to make up the row and column conductors of the LCD. When two sheets overlap a row conductor orthogonal to the column conductor, the rows and columns form a pixel matrix. The row conductor also serves to set the voltage across the cell required for the orientation transition.

An alignment layer, sometimes called an alignment layer, is applied to each sheet. The alignment layer may form parallel fine grooves by a polishing process, which helps to align the liquid crystal molecules in a preferred direction such that the longitudinal axis of the liquid crystal molecules is parallel to the grooves, and the molecules are aligned along the alignment layers. Fix and help to twist the molecules between the alignment layers.

One of the thin sheets is coated with a layer of polymer spacer beads. These beads maintain a uniform gap between the glass sheets where the liquid crystal is actually placed. The two glass sheets are then placed together and the edges are sealed with epoxy. The corners remain unsealed so that the liquid crystal material can be injected under vacuum. When the display is filled with liquid crystal, the corners are sealed and a polarizer (transparent layer with lines) is provided on the exposed glass surface.

The display is completed by connecting row and column conductors to drive circuitry that controls the voltage applied to the various regions of the display.

Flexible displays based on electroluminescence have been presented as wearable devices, and flexible displays based on liquid crystals are currently under study.

Flexible liquid crystal display (LCD) technology enables ultra low power consumption and may even provide features such as zero power image retention. In addition to meeting the requirements of existing low end applications, this display technology is a new market for electronic displays, such as rewritable shelf-edge displays for supermarkets or electronic message stickers. You can carve

Thus, flexible displays can be used for electronic paper, wearable electronics, consumer electronics, displays for portable devices such as mobile phones, portable computers, electronic calendars, electronic books, television or video game controllers, and various other office automatic equipment and audio / video. It can be used for appliances and the like and all other products in which flexible displays can be used.

However, in flexible displays there are many applications where flexible displays are not used in conventional flat locations. Such applications include electronic paper and wearable flexible displays.

When the user observes a flexible display, for example, which may be placed on clothing or placed on various or even variable shaped objects, some of the observed flexible displays may be perceived as flat, while others may be curved It may be recognized. When the flexible display is bent, it has been observed that any undesirable change in emission level and / or color of the flexible display occurs.

Due to the non-rigid structure of the flexible display, the bending of the flexible display causes a change in the cell gap of the flexible display, so that the cell gap in the first portion of the flexible display is It is different from the cell gap in the second part.

During normal operation, the orientation and alignment of the flexible display changes repeatedly, so that changes in warpage and changes in cell gap through the flexible display occur somewhat randomly over time in an unpredictable manner.

These local cell gap changes, where the cell gap in the first portion of the display is different from the cell gap in the second portion of the display, are produced by a flexible display, typically emitted by the pixels of the display. Or a change in color, which results in non-uniform brightness of the displayed image or text. The user may recognize these and other warp related performance characteristics in many ways as a limitation on the potential of flexible displays.

The fact that brightness is one of the most important features of any kind of display is that when the flexible display is bent during normal operation, i.e., the display is bent in various ways that the situation requires, the flexibility characteristic is due to a change in the emission level and / or color. Means little or no, and it is easy to see that it will also make great strides in the field of flexible display technology.

US Pat. No. 5,699,139 to Aastuen and Wenz, entitled "Liquid crystal device having pressure relief structure," incorporated herein by reference, discloses an LCD having an active area for information display and an inactive area adjacent to the active area. Doing. The inactive zone includes a pressure relief zone that relieves the pressure generated in the cell to minimize the effects of pressure changes in the active zone. The display consists of two substrates, at least one of which is flexible, and the two substrates are bonded to the periphery. The plurality of spacers disposed between the substrates evens the gaps between the substrates in the active area. The spacer member is preferably attached to both substrates in the active region, but to one substrate in the inactive region. The pressure relief region acts to relieve the pressure in the display (generally caused by temperature change) by bending the flexible substrate, thereby removing distortion in the active region. The warping of the flexible substrate is improved by including a wedge spacer member that thins the substrate in the pressure relief region or prevents the spacer member from adhering to both substrates in the pressure relief region.

The above-mentioned invention relates to mitigating the pressure generated by changes in temperature in a conventional liquid crystal device, wherein the perceived emission level and / or color in the flexible display caused by the warpage of the display and subsequent associated cell gap changes. There are many shortcomings associated with the problem of reducing the change of

The change in luminescence and / or color caused by the cell gap change due to the bending of the flexible display cannot simply be compensated by providing a pressure relief area that provides constant pressure in the liquid crystal device.

Considering the soft structure of the underlying flexible liquid crystal display, if the flexible display is stressed during the bending of the display, the first dimension of the flexible liquid crystal display cell, e.g. thickness, may decrease, while The same second flexible liquid crystal display cell dimension may be stretched and enlarged during bending of the display. As a result of this metamorphosis, the volume of the flexible liquid crystal display cell becomes constant (and the pressure of the flexible liquid crystal display cell is constant) while the display is curved.

It is also conceivable that as a result of the concave bending of the flexible display, the same pressure as the corresponding convex bending occurs, and there are many other similar effects associated with the concept of symmetry, where a simple pressure relief structure is considered. It is not.

In addition, the introduction of inert pressure relief zones requires physical space, thus placing significant limitations on the resolution of the display and generally reducing overall brightness and performance. This area makes the flexible display bulkier, heavier and difficult to manufacture.

Thus, making the pressure in the cell of the liquid crystal display according to the invention described above constant does not constitute a suitable way to alleviate the problems associated with perceived fluctuations in the luminous level or color in the flexible display depending on the orientation or alignment of the display. .

International patent application PCT / US00 / 05756 to Greene and Krusius, entitled " Compensation for edge effects and cell gap variation in tiled flat-panel, liquid crystal displays, " Procedures are disclosed for correcting spots and variations in brightness due to variations or deformation of materials occurring in other optical, electro-optical, ambient light, electronic, mechanical, and inclined flat panel displays. The purpose of these corrections is to achieve a visually seamless appearance. Temporarily store incoming video data in the input frame buffer memory, perform video processing of the pixel data by reading the video data from the input frame buffer memory and the correction data from the correction data memory with the pixel data processor under the control of the pixel correction control unit Absolute, relative and / or smoothing corrections are made. Also, the pixel correction control unit may be merged with the pixel data processing unit. Corrected pixel data may also be aggregated in the frame buffer memory before being sent to the display.

The arrangement discussed in the above-mentioned international patent application works well and is flat in a tile but discontinuous between tiles so that certain types of cells are associated with a number of drawbacks to the cell gap problem associated with warping effects in flexible displays. Changes in the gap, where brightness and chromaticity changes due to warpage may not necessarily be flat on the display but may occur on the entire display in an unpredictable manner.

The above configuration proposes a method of estimating the matching of absolute brightness and color values with corresponding nominal values, i.e. constant brightness and color distortion, in which the flexible display is bent in different types to have different brightness and color values over time. It does not take into account the fact that it may.

The foregoing arrangement also does not take into account the fact that a change in temperature or pressure that a flexible liquid crystal display can receive during normal operation may change the light emission and color level.

This configuration proposes to experimentally determine the correction data by measuring the transmission as a function of the applied voltage for the pixel in the tile and then comparing it with a nominal predicted value. This will not be feasible for flexible displays because variations in luminance and color require a new transmission measurement to be performed whenever the orientation or alignment (warping) of the liquid crystal flexible display is changed. This method means that the permanent transmission measuring means are integrated with the flexible display, which adversely affects the performance of the flexible display by increasing weight, decreasing flexibility, increasing cost and complexity, and the like.

This configuration also proposes the implementation of a lookup table containing data for individual pixels, which is a bulky memory means requiring a solution that requires both time and processing capacity.

The object of the present invention is to overcome or at least mitigate the above mentioned problems and the limitations of the prior art, which is a device according to claim 1, a flexible display according to claim 11, a portable device according to claim 14 and a method according to claim 16. Is achieved by. Preferred features of the invention are also claimed in the additional dependent claims.

According to a first aspect, the present invention provides a device for compensating for a change in luminescence and / or color in a voltage driven flexible display, the change being related to bending of the flexible display. Measuring means for measuring a cell gap in at least a portion of the sexual display, and adjusting means for adjusting a voltage applied to the portion of the flexible display according to the measured cell gap, wherein the measuring means is configured to repeatedly measure the cell gap. And the adjusting means is associated with a compensating device which is set to iteratively adjust the applied voltage in response to the measured cell gap.

According to another aspect, the present invention relates to a flexible display comprising such a device and a portable device comprising such a flexible display.

According to another aspect, the invention also provides a method of compensating for a change in luminescence and / or color in a voltage driven flexible display, the change being related to bending of the flexible display. A measuring step of measuring a cell gap in at least a portion of the sexual display, and an adjusting step of adjusting a voltage applied to the portion of the flexible display according to the measured cell gap, wherein the steps are repeatedly performed during operation of the flexible display. It relates to the compensation method performed.

The features defined in claims 2 to 5 and 17 to 20 are in particular the advantage that the performance of the compensation means may be adjusted for power consumption and other parameters to provide stable and predictable performance characteristics of luminescence and / or color according to the warping of the display. Has

The features defined in claims 6 to 10 can in particular be minimized as a function of the bending characteristics of the flexible display, in order to optimize the number of measuring means and to minimize power consumption, weight and cost, in particular by the number of points for measuring the cell gap. It has the advantage that it is.

The features defined in claims 11 to 13 have the advantage, in particular, of providing a preferred embodiment of the invention in part.

In general, the present invention relates to new and innovative compensation devices for flexible displays. The present invention is based on the discovery that a change in light emission and color occurs when a liquid crystal type flexible display is bent in various ways. The cause of these changes is the ductility of the materials used to make the flexible displays, which causes cell gap changes in various parts of the flexible display during bending. The change in cell gap affects the switching characteristics of the flexible display, causing it to reflect more or less light than desired. Experiments show that the observed change depends on the warpage. The purpose of the compensation device is to eliminate or at least reduce the effect of the bending of the flexible display on the perceived light emission and / or color.

The obvious solution to this problem is to choose another material that is more resistant to stress and warpage, so that the cell gap is as constant as possible. Instead, the present invention proposes to repeatedly infer the current characteristics of the warpage of the display by measuring the cell gap repeatedly in certain portions of the display and to adjust the voltage applied to the various portions of the display in accordance with the measured cell gap.

While using a flexible display comprising a compensating device according to the invention, the measuring means repeatedly measures the local cell gap at a specific position of the display, and after measuring the cell gap, the observer emits light when the display is bent. Adjust the voltage applied to the display to detect at least or minimal changes in level and / or color.

These and other aspects of the invention will become apparent upon reference to the following detailed description.

Referring to the drawings in conjunction with the following description, it will be understood that the present invention is fully understood.

1 is a schematic diagram of a passive matrix liquid crystal display.

2 is a schematic side view of a portion of a flexible display based on liquid crystals.

3 shows the cell gap as a function of the bending radius in the flexible display.

4 shows the reflection during bending as a function of the applied voltage in the reflective STN display.

FIG. 5 shows the applied voltage at which the reflectance is reduced by 50% relative to its maximum value V50 and the applied voltage at which the reflectance is reduced by 10% relative to its maximum value V10 as a function of the square of 1 / bending radius.

6 is a schematic diagram of a possible layout of the pixels in an active matrix display.

7 is an enlarged cross-sectional view taken along the line VIII-VIII in FIG. 6;

8 is a circuit diagram of an equivalent circuit of a pixel in an active matrix display.

9 is a circuit diagram of an equivalent circuit of the measurement setting of the passive matrix cell gap according to the present invention.

Accordingly, the present invention is directed to variations in luminescence in a flexible display, including but not limited to the brightness and intensity of reflected or transmitted light, and variations in color (but not limited to discoloration, color change, color change, and gray color). Devices and methods for correcting the level), which are mainly associated with the bending of the flexible display. However, these changes may be related to other liquid crystal display cell gap changes or to deformations of materials that may occur in other optical, electro-optical, ambient light, electronic, mechanical and flexible displays.

1 is a schematic diagram of a flexible passive matrix liquid crystal display. The data processor 101 controls a row driver 102 for driving a series of parallel row conductors 103 and a column driver 104 for driving a series of parallel column conductors 105. The data processor 101, row driver 102 and column driver 104 are generally semiconductor based devices.

To address a particular display element (e.g. pixel) within the array, a positive voltage is applied by the row driver at the appropriate row conductor and a negative voltage is applied to the appropriate column conductor (or vice versa), thereby reducing the activation threshold voltage. Excess synthetic RMS voltage is applied across the selected device to activate the liquid crystal material in the device. In order to ensure that the unselected device is not addressed, neither the above positive voltage nor negative voltage alone should exceed the activation threshold voltage. This voltage application process, known as multiplexing, can be repeated until all devices in the display are addressed. As the number of elements or column lines addressed by a common row increases, the voltage difference between the " on " and " off " pixels typically decreases, thereby reducing the contrast.

In many conventional configurations, the row and column conductors are disposed on each substrate on opposite sides of the liquid crystal material. In flexible displays, all connections should be placed on one side of the display. Therefore, the column conductors must be routed in the same plane as the row conductors and vice versa.

2 is a schematic side view of a portion of a flexible display based on liquid crystals. The flexible display includes a top plastic substrate 201 and a bottom plastic substrate 202, each of which has a thickness of 50 to 100 micrometers. A liquid crystal layer 203 having a thickness of 4 to 10 μm is disposed between the upper substrate and the lower substrates 201 and 202. The lithographic spacer 204 is arranged to obtain a uniform cell gap through the flexible liquid crystal display. This lithographic spacer may be formed by spin coating a resistive layer, such as SU8, patterned into pillars, rods, or the like by photolithography in a manner known to those skilled in the art.

FIG. 3 shows the cell gap as a function of the bending radius in a flexible CTLC display. Data was collected using the same flexible display bent at different radii of curvature. Analysis of these measurements revealed that it is possible to predict cell gaps from data on bending radii using the following equations.

(1)

(One)

Here, d represents a cell gap (mu m), d ₀ represents a cell gap (mu m) when the display is not bent, Δ d represents a change in cell gap (mu m) when the display is bent, and a and b Denotes a constant and r denotes a bending radius (mm).

Using equation (1), a = 7.7 (µm) and b = 43.2 ((mm) ² (µm)) are assigned to constants, and the relative change in cell gap during bending is expressed as follows.

(2)

(2)

Here, c represents a constant and c = 9.2 (mm) ² . A relative change of 1% is then obtained at a bending radius of 4 = 30 mm.

Since the electric field applied on the liquid crystal layer is inversely proportional to the cell gap, the electric field increases by 1% when the cell gap decreases by 1%. The liquid crystal material changes the gray level of the pixel in accordance with the increased electric field. In the CTLC display of FIG. 3, the maximum voltage is 25V. To produce 16 gray levels, the voltage must be regulated to within 0.1V per gray level. This is 0.4% of the maximum addressing voltage. Thus, a 1% change in cell gap corresponds to an unacceptable 2.5 gray level.

In passive matrix super twisted nematic (STN) displays, the same problem arises due to the large threshold voltages and steep transmit-voltage curves, which result in very small (relative) voltage spacings per gray level. In an active matrix display, this problem tends to have a higher modulus of elasticity and is a problem that must be performed on the substrate with the high dimensional stability necessary to obtain good alignment of the layers during processing of the active matrix. This will get worse. As a result, a much larger change in cell gap occurs when the display is bent. For flexible E-ink displays, the problem will be greater due to the thick E-ink layer (100-200 microns) required. Thus the intermediate bending line is far from the substrate. Thus, when the display is bent, the change in the associated cell gap will be greater.

4 is a graph showing reflection as a function of applied voltage in a reflective STN display during bending, illustrating the problem that the present invention seeks to solve.

During the experiment (the results of the experiment are shown in FIG. 4), the switching characteristics, i.e. reflection as a function of the applied voltage, are two different from that while the same plastic STN display is aligned in a planar position (bending radius R = 0). While bent to the radius (R = 13 mm and R = 26 mm), it was determined for the same plastic STN display. It can be easily seen that the reflection obtained for any voltage is completely different for different bending radii. Thus, it is impossible to make grayscale by changing the root-mean-square voltage. It is not important whether this voltage is changed by changing the amplitude of the addressing pulse or by changing the pulse width (the method of changing the pulse width is preferred in STN displays). Since the polar / retardation film is aligned outside of a 200 micron thick substrate, it is important that the STN display under consideration is much thicker than the CTLC display (the total thickness of the display (substrate + film) is 2x200). + 2x120 = 640 microns).

FIG. 5 is a graph showing the applied voltage at which the reflectance is reduced by 50% relative to its maximum value v50 and the applied voltage at which the reflectance is reduced by 10% relative to its maximum value V10 as a function of the square of 1 / bending radius. This graph also clarifies the problem that the present invention seeks to solve or at least mitigate. The dependence shown is approximately linear for both parameters, i.e. the slope is the same, thus reducing the switching voltage (or pulse width) by the percentage indicated by dividing 1 by the square of the bending radius, for the bending related cell gap. Compensation can be made.

The previously discussed problem is to measure the physical characteristics associated with the cell gap or pixel gap of a pixel in a flexible voltage driven display and to adjust the voltage applied to the pixel according to the measured cell gap to compensate for the change in cell gap. It is solved or at least alleviated by providing an apparatus and method for doing so.

The cell gap can be measured in several ways. One method is disclosed in US Pat. No. 5,777,596, which is incorporated herein by reference. The display element of the liquid crystal display works like a capacitor. As is known, the charging time of a capacitor circuit is related to the capacitance of the circuit. Thus, measuring the associated charging time (or discharge time) of the display device is an indirect method of measuring the associated capacitance of the device. The measure of the associated capacitance can be used to infer the cell gap.

The liquid crystal display is of the passive matrix type or active matrix type described above. Active matrix displays include a separate electronically controlled switch for each LCD device. This switch may be, for example, a thin film transistor (MOS TFT) disposed adjacent to a corresponding element on a glass substrate. The switch is turned on or off by applying a voltage to or removing the voltage from the control terminal. If a MOS device is used, for example, the control terminal becomes the gate terminal of the MOS device.

6 is a schematic diagram of a portion of a possible layout of a measurement setup in a pixel in an active matrix display. The pixel is defined at the intersection between row conductor 103 and column conductor 105. The pixel is connected to the row conductor 103 and the column conductor 105 by the transistor 601. Lithographic spacers 204 and pixel pads 602 are also shown.

FIG. 7 is an enlarged cross-sectional view taken along the line VIII-VIII of FIG. 6. The row conductor 103 and the column conductor 105 are disposed on the same substrate and separated by the isolation layer 701. On the upper substrate 201 is an unpatterned counter conductor 702 (electrode), which, together with the pixel pad 303, forms a pixel capacitor shown as C _LC in the circuit diagram of FIG.

8 is a circuit diagram of an equivalent circuit of pixels in an active matrix display.

In a typical active matrix display, all switch control terminals are associated with a particular row of the array and are connected to a common row bus. When a voltage is applied to this row bus, each device in that particular row is connected to a corresponding column bus. The voltage may then be passed through the corresponding column bus to each device in the selected row to set the desired display state of each device. The display voltage may be delivered simultaneously or preferably to one column of display elements at a time. A separate display control unit (not shown) synchronizes the transfer of the display voltage.

The display control unit includes, for example, a microprocessor or sequencer that controls the operation and timing of the device, a display memory that stores display data for the entire array, and a line that stores and forwards voltage selection signals for selected rows of the display. It may also include a buffer.

Since the voltage level applied to the corresponding column bus of the display element in the active matrix display is not limited as the voltage level for the passive display, a wide voltage range may be applied to the column bus, and variable intensity may be obtained. In an active matrix device, when a constant voltage is used on the column conductor, the time required to charge the pixel is a measure of its capacitance.

One of the measurement rows is selected first (ie, the transistors in that row are conductive). All pixels in this row are in a standard state prior to selection (eg black: or white). Then, a voltage is applied on all the conductors and the time required for the current through the column conductors to fall below some level is recorded. This provides a measure of the pixel capacitance of all the pixels in the row. When this capacitance is compared with the pixel capacitance in the standard state, the current cell gap can be extracted.

The display is driven line by line. During one frame of time, all rows are selected sequentially by applying a voltage that changes the thin film transistor (TFT) from the non-conducting state to the conducting state. At this line selection time, the pixel capacitor of the selected row is charged to the voltage applied on the column conductor. Another row is addressed for the remainder of the frame time (ie, hold time). The TFT is then brought into a non-conducting state, and the charge on the pixel capacitor must be maintained. In order to suppress visual flicker due to the asymmetry of the work during charging between even and odd frames and to be able to see the video content, the frame rate of the LCD should be at least 50 Hz. In row and column drivers, measurement of pixel capacitance can then be made on the row and column conductors.

For the passive matrix, other methods can be used. The pixels in the measurement row must be in a standard state (eg black or white). An AC signal is then provided on the low conductor. It is best to use a higher frequency than the highest frequency used during addressing of the display. This signal is detected on the column. Thus, the amplitude of the signal on the column conductor relative to the amplitude of the signal supplied on the low conductor becomes a measure of pixel capacitance and can be used to infer cell gaps.

9 is a circuit diagram illustrating an equivalent circuit of a passive matrix cell gap measurement setup according to the present invention.

This display is driven line by line. All rows are selected sequentially by applying a voltage that switches the pixel to mid-grey for one frame time. Then a column voltage is applied that sets the correct gray level for all the pixels in the selected row. The column voltage is too low to affect the switching state of the pixels in the unselected rows. During the remaining frame time, other rows are selected.

Then, at the same location as the row driver and column driver, measurement of pixel capacitance can be done on the row and column conductors.

It is very likely to be used in applications where flexibility in just one direction is high. The reason is that saddle points in the display can be deformed by bending, which leads to high stress levels on the substrate, making it difficult to produce a fully bendable display. An example of a flexible display with flexibility in only one direction is electronic (news) paper, where the display can be stored in the tube and unfolded from the tube by pulling it out of a rigid vertical support.

An embodiment of the present invention of a flexible display having flexibility in only one direction is conceivable. Flexible displays comprising a plurality of long bar-shaped pixel arrays have measurement row means. Since the measurement row has one pixel for each column of the display, it becomes possible to individually compensate for the change in the cell gap for each column. In order to increase the accuracy of the measurement, it is also possible to average over the number of columns in the display. The compensation for the change in cell gap is the scaled column voltage. If the cell gap is reduced by 1%, the column voltage must increase by 1%. In super twisted nematic (STN) and twisted nematic (TN) displays, this relationship is rather difficult due to the change in the twist angle at the change of the cell gap. In this case, a lookup table should be used to find the correct scaling for the column voltage.

For displays with flexibility in all directions, the cell gap should be known for the entire display area. In this case, since they cannot be used to display information at the same time, measurement of the cell gap in the test pixel is not possible. A possible solution is to include cell gap measuring means in the lithographic spacer. This can be done by using a piezo-electric element in the spacer. The piezoelectric element converts the pressure into a voltage difference between its contacts. Since the pressure on the spacer causes the cell gap to change, the voltage difference across the piezoelectric element can be used as an input for gray level compensation.

If one piezoelectric element is included per pixel, it is possible to compensate for each pixel individually or average over a group of pixels in order to increase the accuracy of the cell gap measurement. Another possibility is to include the piezoelectric element at some point in the display to compensate for the gray level for the group of pixels in the display.

A conceivable embodiment is to include one or a plurality of conductive spacers in place of or near some lithographic spacers, for example to provide one or a plurality of measuring conductors (electrodes) on an upper or lower substrate. . It can also be assumed that row or column conductors can be used with such measurement conductors. The conductive spacer portion preferably comprises a piezoelectric element. The change in cell gap causes a change in capacitance between the measuring conductor and the conductive spacer portion, and determining the AC impedance at any number of points by the voltage or current sensor will replace the measurement of the cell gap.

It can also be assumed that the cell gap may be measured at any location within the display, and therefore this data may be combined with information about the structure of the display and its warpage characteristics to compensate for local warpage at various parts of the overall display. . Since the flexible display may be treated as a continuous curved plane, this may be done using, for example, spline interpolation.

Once the cell gap is measured, the adjusting means controls the row and column drivers to adjust the voltage applied to the portion of the display in accordance with the measured cell gap. Such means of adjustment may be carried out in various ways as described above, which are conducive to those skilled in the art.

The repetition frequency of the measurement may be constant, for example 50 Hz, or may vary as a function of user setting, operating conditions or both.

In addition, the adjusting means of the apparatus according to the invention should not be activated unless the measured cell gap change is greater than the determined threshold.

Thus, features of the present invention include measuring means for repeatedly measuring a cell gap in at least a portion of the flexible display and adjusting means for repeatedly adjusting the voltage applied to the wing portion of the flexible display in accordance with the measured cell gap. do.

In the above embodiment, it is proposed to compensate the grayscale error by changing the amplitude of the column voltage. In general, grayscale in an LCD display may be generated by defining a number of subfields during row addressing. The subfields have several lengths within a suitable time (e.g., often a time ratio is chosen such as 1,2,4,8, ...) and the column voltage can be turned on or off during each subfield. The total on / off ratio of the pixels then produces the gray level required for the viewer. Here, it is possible to compensate the gray level by changing the total on / off ratio for the pixel (e.g. selecting several subfields where the column voltage is on or off). If the display can be bent for one constant radius in the row direction, it is also possible to compensate by scaling the length of the subfield.

For passive matrix displays, it is possible to generalize the already proposed gray scale compensation by changing the amplitude of the column voltage. If the display can bend one constant radius in the low direction, a low voltage can be used for gray scale compensation.

The device according to the invention may, for example, be realized as a separate stand-alone unit, or a mobile terminal for a communication network such as GSM, UMTS, GPS, GPRS or DAMPS, or a personal digital assistant (PDA), palmtop computer, It may also be included in or combined with other portable devices of the existing type, such as portable computers, electronic calendars, electronic books, television sets or video game controls, and various other office automatic equipment and audio / video machinery.

The present invention has been described with reference to the above embodiments. However, as defined in the appended claims, other embodiments in addition to the embodiments described above are possible within the scope of the present invention. All terms used in the claims are to be interpreted according to their ordinary meaning in the art, unless specifically defined. Singular elements, means, components, members, units, steps are to be construed broadly as referring to one example thereof. The steps of the methods disclosed herein are not performed in the exact order disclosed unless explicitly indicated.

Claims (20)

An apparatus for compensating for a change in at least one of luminescence and color associated with bending of a fusible display in a voltage driven flexible display, the apparatus comprising: Measuring means for measuring a cell gap in at least a portion of the flexible display; Adjusting means for adjusting a voltage applied to said portion of said flexible display in accordance with said measured cell gap, The measuring means is set to repeatedly measure the cell gap, The adjusting means is set to iteratively adjust the applied voltage in response to the measured cell gap Compensation device. The method of claim 1, Repeat frequency of measurement and repeat frequency of adjustment are constant Compensation device. The method according to claim 1 or 2, At least one of the repetition frequency of the measurement and the repetition frequency of the adjustment is controlled as a function of user setting, operating condition or both Compensation device. The method according to claim 1 or 2, The adjusting means are operated only when a change in the cell gap is detected. Compensation device. The method of claim 4, wherein The adjustment means are activated only when a change in cell gap exceeding a predetermined threshold is detected. Compensation device. The method according to claim 1 or 2, The flexible display is bent in only one direction and the measuring means are distributed along the flexible axis. Compensation device. The method according to claim 1 or 2, The flexible display is bent in two directions, and the measuring means are distributed throughout the flexible display. Compensation device. The method according to claim 1 or 2, At least one measuring means is arranged in at least one lithographic spacer Compensation device. The method according to claim 1 or 2, The number and arrangement of the measuring means is optimized given the flexibility of the display. Compensation device. The method according to claim 1 or 2, The measuring means comprises at least one piezoelectric crystal Compensation device. A device comprising the device according to claim 1. Flexible display. The method of claim 11, The flexible display is an active matrix display comprising a plurality of pixels and a plurality of conductors, The measuring means is set to measure the cell gap in a portion of the display by measuring the time required to charge the pixel when a constant voltage is supplied on the relevant conductor. Flexible display. The method of claim 11, The flexible display is a passive matrix display, The measuring means is set to infer the cell gap by supplying an AC signal to the low conductor and measuring the amplitude of the signal on the column conductor and comparing it with the amplitude of the signal supplied on the relevant conductor. Flexible display. Comprising a flexible display according to claim 11 Portable device. The method of claim 14, The portable device may be one of an electronic paper, a personal digital assistant, a mobile telephone, a set of wearable electronics, a portable computer, an electronic calendar, an electronic book, a television or a video game control. Portable device. In a voltage driven flexible display, a method of compensating for a change in at least one of luminescence and color associated with bending of the fusible display, the method comprising: Measuring the cell gap in at least a portion of the flexible display; And adjusting the voltage applied to the portion of the flexible display in accordance with the measured cell gap, The steps are performed repeatedly during operation of the flexible display. Compensation method. The method of claim 16, Repeat frequency of measurement and repeat frequency of adjustment are constant Compensation method. The method of claim 16, At least one of the repetition frequency of the measurement and the repetition frequency of the adjustment is controlled as a function of user setting, operating condition or both Compensation method. The method according to any one of claims 16 to 18, The adjusting step is performed only when a change in the cell gap is detected. Compensation method. The method of claim 19, The adjusting step is performed only when a change in cell gap exceeding a predetermined threshold is detected. Compensation method.

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